Former Anglo Irish Bank chief David Drumm is being held in solitary confinement following threats to his personal safety.

The banker has been transferred without notice between four prisons in two states in the US after authorities became aware that he was at risk behind bars.

Details relating to "a series of highly unusual past and ongoing incidents" in which Mr Drumm has been targeted while in custody are contained in documents supporting a petition for habeas corpus filed with the Massachusetts District Court on Christmas Eve.

Lawyers for the former banker are seeking his release, claiming he is being unlawfully detained.

Highlighting the dangers Mr Drumm has been exposed to since his arrest by US Marshals last October on foot of an extradition warrant from Irish authorities, the filing states: "A series of highly unusual past and ongoing incidents . . . have created a legitimate risk to Mr Drumm's safety as an inmate of the various facilities he has been housed in over the past three months.

"As a result of those risks, Mr Drumm has been held under solitary confinement and transferred, with no notice, to four different facilities in two states and multiple times within various units of such facilities."

While Mr Drumm's legal team have made reference in open court to his personal safety being threatened, the precise nature of the threats against him has not been disclosed until now.

Elsewhere in the petition filed on December 24, lawyers for Mr Drumm argue that Judge Donald Cabell erred in his decision last month not to release him on bail in advance of his extradition hearing which is due to get under way in March.

In their submission, they say that in addition to failing to take into account the risks posed to Mr Drumm's personal safety, Judge Cabell had understated the impact of the banker's incarceration on his wife, Lorraine, and their two daughters.

Mr Drumm is seeking to prevent his extradition from the United States to face 33 criminal charges relating to transactions that took place at Anglo Irish Bank in the lead-up to the 2008 financial crisis.

He is currently being held in the Plymouth County Correctional Facility just outside Boston.

Before that became known, the only other publicly-available information in relation to his whereabouts had referred to his incarceration at the Donald W Wyatt Detention facility in Rhode Island.

Mr Drumm (49), who has been given the prisoner number 68201, is expected to remain at the prison until at least March, when his extradition case is due to be heard.

He has been in custody since being arrested at his $2m (€1.75m) home on the outskirts of Boston on October 10.

The decision to deny him bail was a major blow to Mr Drumm, who had offered to be placed under house arrest and electronically monitored.

During his failed bail application, he expressed unhappiness with the regime at the prison, describing conditions as "uncomfortable", which made it difficult to meet his lawyers.

However, a judge ruled that the fact that jail is unpleasant did not amount to a special circumstance permitting release.

He was also denied bail because he was considered a flight risk after the judge found his background and experience in international matters, as well as the presumption that he had substantial assets at his disposal, provided him with the ability to flee if he was so inclined.

The judge said the bankruptcy court's finding that Mr Drumm intentionally failed to disclose substantial assets to investigators in order to mislead them had a bearing on his decision not to grant bail.

Last month, Mr Drumm personally pleaded with the US judge to release him on bail, stressing that he did not flee Ireland after he resigned from the helm of Anglo Irish Bank in December 2008.